list.c

//a trivial doubly-linked list implementation

#include <stdio.h>
#include <stdlib.h>

typedef struct Node {
    struct Node* next;
    struct Node* previous;

    int value;
} Node;

typedef struct List {
    Node* head;
    Node* tail;

    int length;
} List;

List* create_list () {
    List* ret = malloc(sizeof(List));
    //yeah, I should check that there was enough memory, blah blah
    //but seriously, fuck that

    ret->head = NULL;
    ret->tail = NULL;
    ret->length = 0;

    return ret;
}
void destroy_list (List* lst) {
    Node* node = lst->head;

    while (node) {
        Node* next = node->next;
        free(node);
        node = next;
    }

    free(lst);
}

void print_node_chain (Node* node) {
    printf("%d", node->value);
    if (node->next) {
        printf(" <-> ");
        print_node_chain(node->next);
    }
}
void print_list (List* lst) {
    Node* node = lst->head;
    if (!node) {
        return;
    }

    print_node_chain(node);
    printf("\n");
}

void print_list_range (List* lst) {
    if (!lst->head || !lst->tail) {
        printf("Can't print the range without nodes");
        return;
    }

    printf("[%d, %d]\n", lst->head->value, lst->tail->value);
}

Node* add_value (List* lst, int val) {
    Node* node = malloc(sizeof(Node));
    node->value = val;
    node->next = lst->head;

    if (lst->head) {
        lst->head->previous = node;
    }
    if (lst->tail == NULL) {
        lst->tail = node;
    }

    lst->head = node;
    lst->length += 1;

    return node;
}

void remove_value (List* parent, Node* node) {
    //unlink the node from its siblings
    //imagine the beginning state is
    // 3 <-> node <-> 5
    if (node->previous) {
        //we unlink 3 from node, and link it to 5
        // 3 ---------> 5
        // ^---node <---^
        //note that 5 is not yet connected to 3. that's fixed in the next if
        node->previous->next = node->next;
    }
    if (node->next) {
        //we unlink 5 from node, and link it to 3
        // 3 <------> 5
        // ^---node---^
        //which, after freeing the node, simply looks like
        // 3 <-> 5
        node->next->previous = node->previous;
    }

    if (parent->head == node) {
        parent->head = node->next;
    }
    if (parent->tail == node) {
        parent->tail = node->previous;
    }

    parent->length -= 1;

    free(node);
}

void print_list_stuff (List* lst) {
    printf("%d\n", lst->length);
    print_list(lst);
    print_list_range(lst);
}

void main () {
    List* lst = create_list();

    Node* p0 = add_value(lst, 14);
    Node* p1 = add_value(lst, 42);
    Node* p2 = add_value(lst, -4);

    print_list_stuff(lst);

    remove_value(lst, p2);
    print_list_stuff(lst);

    destroy_list(lst);
}